10.1 Energized
10.1.1 High-pressure water 10.1.1.1 Hand-held nozzle
The resistivity of water from the wash truck reservoir should be checked by a portable resistance meter each time water is added. The wash truck should be positioned so that the wash hose will come off the hose reels at the tower leg to be climbed. In this way, the hose does not have to be dragged around the tower.
Some utilities specify wire braid conductive hose and bond the truck to the tower. The continuity of this bonded connection is checked prior to the start of the job. Routinely, all bonding connections should be
checked for corrosion and cleaned, as required. Since the wash truck may acquire a relatively high potential, it is important when washing that no person gets on or off the truck and that all persons on the ground are kept away from the truck. Persons on the truck shall also avoid reaching out and touching adjacent trees, poles, towers, or other objects.
Some utilities use nonconductive wash hose and do not bond the truck to the tower so that the truck is unlikely to acquire a high potential. However, good practice is to not allow anyone to get on or off the truck and to keep all persons on the ground away from the truck during the actual washing operation.
Next, the line worker should climb the tower carrying a hand line. The truck driver should send up the hose, gun, and nozzle. The line worker should bond the nozzle to the tower steel or pole bond wire.
The line worker should then direct the truck driver to increase the water pressure. If the unit is equipped with a demand throttle, the pressure (revolution per minute) will be automatically increased when the gun is opened. The water is directed away from the insulator string until full pressure has been achieved. The line worker on the tower should then direct the wash stream at the insulator. The nozzle to conductor distance shall not be less than the established minimum wash distance (see tables 3 and 4). Suspension insulator strings are washed by first directing the stream of water at the insulator nearest the energized conductor in such a manner as to take advantage of both the impact and the swirling action of the water to remove depos-its. After the bottom insulators in the string are washed, the wash stream should be moved up a few undepos-its.
After these units are washed, the stream should be directed on the clean units below to rerinse them. This process should be repeated, moving up a few insulators at a time until the entire string is clean. Failure to rerinse lower insulators before moving further up the string can lead to flashover. The stream shall be moved away from any energized part of insulators before the water pressure is reduced. Care should be taken to pre-vent the spray from unduly moistening nearby dirty insulators, particularly in the station.
Dead-end insulators shall be washed carefully to keep overspray from causing flashover. Begin washing on the downwind end of the insulator string and then work upwind.
It is important that the above procedures and the established wash parameters are strictly adhered to when conducting hot-line washing.
10.1.1.2 Remote-control nozzle
The technique for washing with a remote-control nozzle is very similar to that for the hand-held nozzle. The primary difference in the two techniques is that the nozzle positioning is done remotely from an operator’s console at the base of the truck boom. A knowledgeable operator is required to position the boom in a loca-tion that will provide a good washing angle in addiloca-tion to maintaining safe working clearances.
10.1.1.3 Fixed-spray nozzle
Fixed-spray nozzle hot-line washing has proven to be effective in preventing sea-salt contamination flash-over problems.
The wash parameters and equipment should be developed and established for each installation. This is mainly due to various local parameters that influence the washing. Such parameters are precipitation, water resistivity, wind, contamination severity, and design and installation arrangement of the insulators to be washed.
10.1.2 Compressed air cleaning
The technique for this method is very similar to that for high-pressure washing. The insulators next to the con-ductor are cleaned first (one or two insulators on each string of a vee string). Then, the remainder of the
insula-tors are cleaned, moving away from the conductor. A full stream of cleaner should be flowing before the stream contacts the conductor and likewise, a decrease in psi should only be made after leaving the conductor.
10.1.3 Hot wiping
Normal care shall be taken to observe the safe working distances for the hot sticks. The critical precaution is to keep the wiping cloths clear of any grounded objects or supports. When two sticks are used, good commu-nication and coordination is required between operators.
10.1.4 Helicopter
The actual washing techniques employed are similar to those for washing with the hand-held nozzle. A knowledgeable pilot, or pilot/wash operator team, is required to position the aircraft/wash-boom in a loca-tion that will provide a good washing angle in addiloca-tion to maintaining safe working clearances to other phases, tower equipment, and/or obstructions. Three techniques have been employed when using water to wash or clean insulation contamination.
10.1.4.1 Fixed nozzle
A fixed nozzle is extended from the helicopter along the path of a runner or guide to outside the direct prop wash. The pilot controls the direction of the water stream by movement of the helicopter. The pilot controls the water stream pump as necessary.
10.1.4.2 Movable nozzle on a fixed wand
This system is similar to the fixed nozzle except the single pilot controls a movable nozzle. The helicopter is moved to the general location and the movable nozzle controls the direction of the water stream.
10.1.4.3 Fixed nozzle in a movable wand
This method employs a second person to control the direction and availability of the water stream. The heli-copter gets to the required general position and then washing is actually controlled by the second person.
Each of the three methods have their advantages and can be used on transmission circuits effectively. The greatest plus for helicopter cleaning is its production and easy access to isolated structures. However, the expense and special equipment required suggest the importance of careful analysis of the cost to benefits before considering everyday use.
10.2 De-energized
All of the techniques discussed in 10.1 can be utilized when the facility is de-energized. In addition, hand cleaning and low-pressure water technique described elsewhere may be used. When the system is de-ener-gized, the requirements of water resistivity and clearances are relaxed, thereby allowing different washing conditions.
10.2.1 Low-pressure water fixed-spray nozzle
Fixed-spray-nozzle washing has proven to be effective in preventing sea-salt contamination flashover prob-lems. This method of washing is used widely in Japan.
The wash parameters and equipment shall be developed and established for each installation. This is mainly due to various local parameters that influence the washing. Such parameters are precipitation, water resistiv-ity, wind, contamination severresistiv-ity, and design and installation arrangement of the insulators to be washed.
10.2.2 Hand cleaning
The techniques required for hand wiping are dependent upon the nature of the surface deposits to be removed. Some insulators can be cleaned by using only soft dry wiping rags. Additional materials, such as wet or paraffin-soaked cloth, solvents, steel brushes, or steel wool, may be needed for other insulators.
10.3 Results
Results of efficient insulator cleaning can be judged by
a) Visible (clean-shiny). Surface condition of both the top and bottom of the insulator skirts should be visually clean and shiny after the water or solvents have dried.
b) Insulator vibration (ringing). Mechanical vibration (ringing) of insulator skirts under impact of high-pressure washing and exhibiting evidence of efficient swirling cleaning action.
c) Absence of corona. Blue corona discharges extend from the metal cap to the porcelain during ener-gized high-pressure washing and may be heard for a few seconds after completion of cleaning.
If this discharge continues for more than a few seconds it may indicate incomplete washing of the insulators, in which case the wash stream should be reapplied.
d) Clarity of runoff. Clarity of the water runoff may also indicate the effectiveness of contamination removal. Clarity of water runoff may be difficult to observe due to distance, sunlight, wearing of sunglasses, etc.
10.4 Frequency of cleaning
Frequency of cleaning varies depending upon the degree of contamination, the weather conditions, and the particular insulator design. Where frequent washing is required, it is sometimes economical to install either piping systems on towers or permanent fixed-spray nozzle systems for ease in washing.
Insulators should be washed prior to the time of reaching the critical contamination level. This point can be estimated from
a) Past experience on periods between flashovers or pole fires
b) Allowable equivalent salt-deposited density (ESDD) obtained from de-energized test insulators or from energized insulators
c) Degree of scintillation during damp weather conditions d) Complaints of radio interference
e) Proximity and exposure to the pollution source
f) Type of contaminant, and its rate of buildup on the insulator
g) Weather conditions (it is noted that the danger of flashover and pole fires is particularly great after a long, dry period, either in winter or summer, followed by a light drizzle or fog condition)
h) Sensor insulators that indicate contamination level (to be used for areas of consistent contamination levels or worst-case areas)